Conventionally, for increasing the thermal storage capacity of a water tank for storing heat using the sensible heat of water, there is a related art of immersing large number of thermal storage body in the water in the tank. That type of related art has an advantage of increasing the thermal storage capacity utilizing existing water tank being used to store heat.
An examples of the above-described thermal storage body is a hermetically sealed container containing a thermal storage medium which solidifies at or above the water-solidification temperature, that's to say, 0° C. or above, such as various kinds of wax. In the process, thermal storage medium is solidified before water solidifies, thus utilizing the latent heat of the thermal storage medium to increase the thermal storage capacity.
However, that type of cooling medium body has a drawback. In the above-mentioned process, when the thermal storage medium in the cooling medium body solidifies, no fluidization of the thermal storage medium occurs, inside the thermal storage medium body. Furthermore, because of the low thermal conductivity of the solidified thermal storage medium, the efficiency of heat exchange reduces, between the water in the water tank and the thermal storage medium.
To prevent the drawback, there is a countermeasure to decrease the size of container, which has the cooling medium body, and to increase the surface area relative to the volume. The method, however, needs to charge a vast number of thermal storage bodies into the water tank. Thus, in case of using a large-sized water tank, a vast number of thermal storage bodies are required.
In the above-described water tank or the like for storing heat, the temperature of internal thermal storage medium, or water, varies with various conditions. For example, the thermal storage temperature is necessary to be changed depending on the kind of refrigerating machine that cools the water in the water tank, or depending on the usage of the thermal load side that utilizes the water of the water tank as the thermal storage tank.
Accordingly, the conventional thermal storage medium such as one kind of wax is not suitable for attaining thermal storage temperature in various kinds of usage because of fixed solidification temperature thereof. As a result, the thermal storage temperature of the above-described water in the water tank has the restricted range.
Furthermore, from the viewpoint of the thermal storage medium of the related art as a thermal storage apparatus, various kinds of apparatus for thermal storage medium are used in air-conditioners and the like. The thermal storage medium are used to store discontinuously supplied energy such as midnight power and waste heat generated in plants, thus to effectively use energy by utilizing thus stored cold heat at air-conditioners.
The apparatus, which uses ice, is known as one of the thermal storage medium apparatus in the world. In the apparatus, which makes use of the ice, the ice is produced during midnight time by utilizing midnight power and the like, and the cold thermal stored heat is utilized at air-conditioners during daytime. Compared with the apparatus by thermal storage medium, which utilizes sensible heat of water, the ice-used thermal storage medium has an advantage of capable of storing a large amount of the cold thermal capacity owing to the latent heat of the ice. In order to produce the ice, however, water requires to be cooled to a further low temperature than the solidification temperature thereof. On the contrary, the solidification temperature of the water is low. Therefore, the coefficient of performance of the refrigerating machine degrades. In addition, the ice and the ice slurry are difficult in handling and transporting, so the apparatus becomes complex and large.
From another point of view, there is a thermal storage medium body made of gas hydrate, which is disclosed in, for example, JP-A-2-203138, (the term “JP-A” referred herein signifies the “unexamined Japanese patent publication”). The technology disclosed in the patent publication, however, uses chlorofluorocarbon-base refrigerant R11 as the coolant for generating gas hydrate. The R11 is a compound having large ozone depletion potential, and exists as gas phase under atmospheric pressure, thus a hermetically sealed container requires, which raises a problem to needs the expensive apparatus using the thermal storage medium.